1. Field of the Invention
The present invention relates to a composite type microphone that incorporates a plurality of microphone units of different electroacoustic conversion methods into a common microphone body, e.g., the composite type microphone capable of disposing a condenser microphone unit in a front acoustic terminal portion of a dynamic microphone unit.
2. Related Background of the Invention
In recording a sound generated from the same musical instrument or the like, microphones of different electroacoustic conversion methods, e.g., a dynamic microphone and a condenser microphone, are sometimes disposed side by side for use. This is intended to record a sound from the same sound source with a plurality of microphones of different conversion methods and mix the output signals of the respective microphones, thereby taking advantage of the characteristics of the respective microphones, because the microphones of different electroacoustic conversion methods have mutually different sound quality. In particular, such recording form is often employed in recording a bass drum.
In case of attempting to record a sound coming from the same sound source with a plurality of microphones of different conversion methods as described above, since a phase difference occurs in the output signals of both microphones depending on the relative installation position relation between both microphones, the relative installation position of the plurality of microphones is carefully determined so as not to cause a phase difference. When a player plays a musical instrument, however, there is a drawback that a stand supporting the microphone vibrates, the installation position of microphone will shift with this vibration and the initial installation position can not be maintained, resulting in a phase difference in the output signals of the mutual microphones.
In order to solve such positional shift problem, composite type microphones are put in practical use. The conventional composite type microphone is made by disposing microphone units of mutually different electroacoustic conversion methods, e.g., a dynamic microphone unit and a condenser microphone unit, in parallel within a single microphone body to position vibrating plates of both microphone units on the same plane. According to such conventional composite type microphone, even if the installation position of the microphone has shifted due to playing of a musical instrument and the like, the mutual positional relation between two microphone units incorporated in the microphone body will not shift and thus the mutual phase of the output signals from two microphone units will not shift.
However, since the conventional composite type microphone is made by disposing two microphone units in parallel to integrate, a drawback is that the microphone is increased in size in the diameter direction. Since the upsized microphone is difficult to install and increases its weight, a drawback is that the microphone stand also needs to have a robust structure, thus increasing its weight and causing a difficulty in handling.
In addition, as a known art related to the composite type microphone, there is a microphone made by combining a bone-conduction microphone and an air-conduction microphone, which is used under noise environment. Such type of composite type microphone includes a combining control circuit for combining the output component of bone conduction from the bone-conduction microphone and the output component of air conduction from the air-conduction microphone. A combining control circuit is proposed, which includes a noise-level measurement unit for measuring the external noise level, and is configured to carry out a control of increasing a ratio of the output component of air conduction to the output component of bone conduction when the external noise level measured by this measurement unit is small, and decreasing the ratio of the output component of air conduction to the output component of bone conduction when the external noise level is high, so that the mixing ratio of the output component of bone conduction and the output component of air conduction is maintained appropriately even under fluctuation of the external noise (e.g., see Japanese Patent Application Laid-Open No. 8-214391).
The invention described in Japanese Patent Application Laid-Open No. 8-214391 however differs from the present invention in the problem to be solved and in the means for solving the problem.
As a known art related to the composite type microphone, there is also a composite type microphone made by integrating an FM wireless microphone circuitry and an optical wireless microphone circuitry. This is a wireless microphone device which accommodates the FM wireless microphone circuitry and the optical wireless microphone circuitry in the same housing, wherein an optical system of a high sound quality and a radio wave system capable of providing a long propagation distance are shared by means of a combination of a multiplication circuitry, a frequency conversion circuitry, and a PLL circuitry (e.g., see Japanese Patent Application Laid-Open No. 10-75497).
The invention described in Japanese Patent Application Laid-Open No. 10-75497 however differs from the present invention in the problems to be solved and in the means for solving the problems.